Question

A machine gun is mounted on a flat railroad car. The gun is firing bullets at the rate of 10 bullets per second each of mass 10 g. The bullets are fired at velocity 500 ms^-1 relative to the car. Calculate the acceleration and force of car at the instant when its mass is 200 kg.

• A. 0.25 ms^-2, 50 N
• B. 2.5 ms^-2, 500 N
• C. 25 ms^-2, 50 N
• D. 8 ms^-2, 1600 N

Answer 1

Answer: (A)

0.25 ms^-2, 50 N

Answer 2

Here, reacting force = relative velocity × $\frac{mass}{time}$ = 500 × $\left( \frac{10 \times 10}{1000} \right) = 50N$ (taking time = 1 s)

Using F = ma, we get

a = $\frac{F}{m} = \frac{50}{200}$ = 0.25 ms^-2